如何獲取已經在另一個 class 中設置的實例值？

Question

我是 Java 的新手。 我有 3 個類：1-DataHolder 2-SetToDateHolder 3-GetFromDataHolder； In the "SetToDateHolder" class, I set the value to dataholder object, and I trying to access it in the "GetFromDataHolder" class, but it got null value, I know it happens because of new instance created. 你能幫我意識到我可以得到我在另一個 class 中設置的實例的值。

這些是類：

public class DataHolder {

    private String myName;

    public String getMyName() {
        return myName;
    }

    public void setMyName(String myName) {
        this.myName = myName;
    }
}

public class SetToDataHolder {

    public static void main(String[] args) {
        DataHolder dataHolder = new DataHolder();
        dataHolder.setMyName("Wesley");
    }

}

public class GetFromDataHolder{
    
    public static void main(String[] args) {
        DataHolder dataHolder = new DataHolder();
        System.out.println(dataHolder.getMyName());
    }

}

Answer 1

我真的不明白為什么你需要 2 個額外的類，因為你的 DataHolder class 中已經有了 getter / setter，但這里是你應該如何繼續你的邏輯：

public class DataHolder {

    private String myName;

    public String getMyName() {
        return myName;
    }

    public void setMyName(String myName) {
        this.myName = myName;
    }
}

public class SetToDataHolder {
    
    private DataHolder dataHolder;

    public SetToDataHolder(DataHolder dataHolder){
        this.dataHolder = dataHolder;
    }

    public void setMyName(String myName) {
        this.dataHolder.setMyName(myName);
    }
}

public class GetFromDataHolder{
    
    private DataHolder dataHolder;

    public GetFromDataHolder(DataHolder dataHolder){
        this.dataHolder = dataHolder;
    }

    public String getMyName() {
        this.dataHolder.getMyName();
    }
}

public class MainClass{
    
    public static void main(String[] args){
        DataHolder dataHolder = new DataHolder();

        SetToDataHolder setToDataHolder = new SetToDataHolder(dataHolder);
        setToDataHolder.setMyName("Wesley");

        GetFromDataHolder getFromDataHolder = new GetFromDataHolder(dataHolder);
        System.out.println(getFromDataHolder.getMyName());
    }
}

這個想法是您的 SetToDataHolder 和 GetFromDataHolder 可以訪問相同的 DataHolder 實例。